For information purposes only: in case of someone need to convert date format from C# to Ext, please use Ext.Net.Utilities.DateTimeUtils.ConvertNetToPHP method, as shown bellow:
Code:string formatConverted = Ext.Net.Utilities.DateTimeUtils.ConvertNetToPHP("dd/MM/yyyy HH:mm:ss", null);
//formatConverted = d/m/Y H:i:s